Diesel Particulate Filters
Discuss about the Methods of Controlling Emissions in IC Engines.
The milestones achieved in global economy in regards to clean energy despite the eminent climatic change has sparked a number of research activities in the industrial world with the view of investing more on the alternative sources of energy. Owing to the fact that automobiles are presently a chief source of air pollution, major automotive firms and state governments are working together to offer a solution that will lead to the decline of vehicle emissions and a corresponding decrease in the utilization of fossil fuel. Various manufacturers have in the recent past embarked on research on the different methods of reducing the overreliance on fossil fuel and the need to come up with sources of alternative power. Such milestones in the research include the electrically propelled vehicle engines and the internal combustion (IC) engine vehicles. Some of the commonly used fuels in the present times for the IC engine vehicle are natural gas, methanol, diesel, gasoline, and supercharging and turbo charging gasoline. One of the reasons for the widespread utilization of IC engine is that the high-energy content can be easily transported. However, its major drawback is that the combustion of fuels results to hazardous emissions to the environment. The aim of this paper is to establish the ways of controlling such emissions in an IC engine. The main pollutants generated by the IC engines are carbon monoxide, NOX, noncombustible hydrocarbons, and other emissions in particulate form. All fuel-combusting systems emit carbon dioxide in enormous volumes that result to green house effect.
Diesel Particulate Filters
Since 2000, Diesel Particulate Filters have been used in manufacturing of vehicles. Since the development of the Euro 5 norm, the technology has been used as a standard device on all new diesel cars among the European nations (Favre, May& Bosteels, 2011). Some buses and trucks that bear the euro 5 norm emissions standards were installed the diesel particulate filters to meet the requirements of the number of emissions of mass and particle. The figure below shows a wall-flow DPF.
Figure 1wall-flow DPF
Catalyst Control Technologies
The principle by which this method operates in controlling the gaseous emissions from an IC engine is based on chemical catalysis process. The catalyst results to chemical reactions without being consumed or changed. The catalytic control system constitutes a steel housing with a size that depends on the engine size where it is contained. The steel housing bears a ceramic or metallic structure that acts as a catalyst substrate or support. The figure below shows ceramic substrates.
Catalyst Control Technologies
Figure 2 ceramic substrates
The engine steel housing does not have any moving parts. It only has its substrate interior surfaces coated with base metals. In some other cases, the interior surface is coated with precious catalytic metallic elements like vanadium, palladium, and platinum and this relies on the pollutants targeted.
Catalysts convert pollutants into non-toxic gases by generating chemical reactions within the exhaust stream. Such reactions vary based on the technology being employed (Sharaf, 2013). In addition, the technology adopted depends on whether the engine is working under stoichiometric, lean, or rich conditions. At any rate, the catalysts in emission control are aimed at eliminating nitrogen oxide gas, carbon dioxide, and others pollutant matter to differing degrees. The choice of the method of an emission control for gaseous emissions relies on the operating mode of the engine such as load and speed, the engine type, and the targeted pollutants. In some cases that involve rich burn engines, the oxides of nitrogen may be the only emission that is controlled. In such a case, there may be minimum reduction in carbon monoxide. On the contrary, in the scenario of lean burn and stoichiometric engines, considerable reductions in all the three major pollutants can be attained.
Various emission control methods have to be used in stationary IC engines based on the air to fuel ratio of the engine. The reason is that the composition of the exhaust gas varies based on the operating condition of the engine such as stoichiometric burn, lean or rich. The operating mode of the engine such as its load and speed should be considered since this affects the temperature of the exhaust gas.
This method is capable of achieving considerable reductions of oxides of nitrogen for rich burn engines. In a case where the engine operates as stoichiometric point (ë=1) the technology is termed three-way catalyst (Sharaf, 2013). In such a case, other emissions are reduced apart from the oxides of nitrogen such as carbon monoxide. On the other hand, lean oxides of nitrogen and oxidation catalysts offer a minimal or no emission control in a rich-burn condition. Notwithstanding, in a lean-burn condition, oxidation catalysts offer a substantial reduction in both the oxides of nitrogen and carbon monoxide.
For more than fifteen years, the method has been employed in controlling NOx emissions generated by the rich-burn engines. When used, the IC engines have shown the capacity to realize over 98 % reduction in emissions (Sharaf, 2013). More than three thousand rich-burn IC engines have been fitted with this technology as a technique of controlling the nitrogen oxide emissions from lean-burn stationary Internal Combustion engines. The method was first adopted in the United States and since that time, it has continued to gain popularity.
Non-selective catalytic reduction
Lean-burn engines are known to generate exhaust rich in oxygen and this makes the reduction of nitrogen dioxide typically impracticable when non-selective catalyst technology is employed. On the other hand, the introduction of a reducing agent like urea or ammonia and other agents aid in the chemical reaction. The reaction is as shown below.
The reactions that take place when the reducing agents are used leads to the reduction of nitrogen oxide emissions by more than 90% (Heck & Farrauto, 2001). Such a method is known as selective catalytic reduction since the catalyst only aims at reducing the oxides of nitrogen. The diagram below shows a selective catalytic reduction.
Figure 3 selective catalytic reduction
According to Kumar and Rehman (2011), the HCCI technology can reduce the particulate matter and NOx emissions by the spark ignition and compression combustion engines that use fossil fuels. This is possible by the application of two significant processes. The first process involves the auto ignition of the NOx and Particulate matter mixture as a result of the compression heat. The second process involves the formation of a homogenous mixture of NOx and particulate matter found in the diesel fuels. According to Jin and Zheng (2015), the homogenous mixture is achieved by port injection. The only challenges however, are the viscous nature of the diesel fuel, high octane number, and a broad range of the boiling points. This has an impact of prolonged mixing time of the diesel fuel to form a homogenous mixture whereas; the time taken for chemical ignition is short. In addition, there is the challenge of fuel wetting owing to the nature of the diesel fuel.
According to Alagumalai (2014), one of the future prospects in emission control in IC engines is technology forcing. The author argues that in this approach, the regulatory agency establishes certain requirements to ensure a limit on the amount of emissions allowed over a particular period using indeterminate technology. In most cases, such technologies have not been fully exploited or fully utilized or used widely on commercial basis despite pilot demonstrations and experimentation. Such efforts are aimed at cutting down the automobile emissions responsible for greenhouse effect such as carbon dioxide that for the last 40 years have doubled, with the highest global contributors being the United States and China (Alagumalai, 2014).
The second emerging trend in the reduction of emissions by the automobile industry is the use of bio-fuels to replace the fossil fuels such as petrol and diesel. According to (Alagumalai, 2014), the research conducted by the Swiss Federal Laboratories for Materials Science and Technology on the bio-fuels have demonstrated potential cost and environmental benefits of such a fuel in the IC engines. The author mentions that the research revealed the ability of the bio-fuels to minimize the greenhouse emissions by the IC engines by 50% as opposed to fossil fuels. Payri et al. (2014) corroborates that bio-fuels can significantly reduce the impact of GHG on the IC engines owing to its cost-effectiveness similar to that of electrical engines but with much reduced increment in the lifetime cost. The author also mentions that countries like Brazil have already implemented the laws that increase the bio-fuel share.
Selective Catalytic Reduction
The third emerging trend in the reduction of emission of greenhouse gases such as carbon dioxide by the automobile engines is the adoption of Hybrid Electrical Vehicles (HEV) and Electrical Vehicles (EV). According to Payri et al. (2014), the two technologies can achieve this aim using electricity production mix. In the present times, European countries, Japan, and the United States are the leading in the adoption of the EV and HEV technologies. The report released by the European Automobile Manufacturers’ Association shows that between 2020 and 2025, the market share for the EV and HEV engines will rise between 3 to 10%.
There have been great achievements the in global economy in relation to clean energy in spite of the inevitable climatic change. These have significantly resulted to a number of research attempts in the automobile space across the globe with the aim of investing more on the subsidiary sources of energy. Because the automobile engines are presently the major air pollutants, majority of the automotive firms and state governments across the globe are collaborating to offer a solution that will result to the control of automobile emissions of carbon dioxide and other exhaust gases and analogous decrease in the consumption of fossil fuels such as gasoline and petrol. The quantity of carbon dioxide passed off from the automobile sector accounts for an average of 20 percent of the entire amount of carbon dioxide released to the atmosphere globally. As a result, because of the need to control or manage global warming, there is a corresponding need to control this percentage to a manageable amount in the atmosphere. There is commonly a great amount of carbon dioxide released by the automobile sector and this continually leads to stringent standards of fuel economy globally. This sequentially necessitates improvement of fuel economy by the automobile engines. Some of the technologies commonly used to cut down emissions by the IC engines include Diesel Particulate Filters, homogenous charge compression ignition (HCCI), and Catalyst Control Technologies. However, each of the methods have their drawbacks and this means there is need for future developments and innovations to come up with the potential ways of reducing emissions in IC engines. In terms of the future prospects of IC engines, there are emerging trends such as technology forcing, replacement of fossil fuels with bio-fuels, and adoption of EV and HEV engines to reduce the greenhouse emissions by the IC engines.
Alagumalai, A 2014, Internal combustion engines: Progress and prospects, Renewable and Sustainable Energy Reviews, 38, pp. 561-571.
Favre, C., May, J. and Bosteels, D 2011, Emissions Control Technologies to Meet Current and Future European Vehicle Emissions Legislation, Association for Emissions Control by Catalyst (AECC) AISBL, Brussels, 20, p. l-12.
Heck, R.M. & Farrauto, R.J 2001, Automobile exhaust catalysts, Applied Catalysis A: General, 221(1), pp. 443-457.
Jin, C. and Zheng, Z 2015, A Review on Homogeneous Charge Compression Ignition and Low Temperature Combustion by Optical Diagnostics, Journal of Chemistry, 2015, pp. 1-23.
Kumar, P. & Rehman, A 2011, Homogeneous Charge Compression Ignition (HCCI) Engine Technology-A Review, International Journal of Current Engineering and Technology, 11(6), pp. 47-67.
Payri, F., Luján, J., Guardiola, C. and Pla, B 2014, A Challenging Future for the IC Engine: New Technologies and the Control Role, Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles, 70(1), pp. 15-30.
Sharaf, J 2013, Exhaust emissions and its control technology for an internal combustion engines, International Journal of Engineering Research and Applications, 3(5).
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